, are of little value, others are
limited in their applications; others again are so well suited to
particular purposes that their use is almost entirely restricted to
such.

The sterilising agents in common use are:

~Chemical Reagents.~--_Disinfectants_ (for the disinfection of glass and
metal apparatus and of morbid tissues).

~Physical Agents.~ HEAT.--(a) _Dry Heat:_

1. Naked flame (for the sterilisation of platinum needles, etc.).

2. Muffle furnace (for the sterilisation of filter candles, and for the
destruction of morbid tissues).

3. Hot air (for the sterilisation of all glassware and of metal
apparatus).

(b) _Moist Heat:_

1. Water at 56 deg. C. (for the sterilisation of certain albuminous
fluids).

2. Water at 100 deg. C. (for the sterilisation of surgical instruments,
rubber tubing, and stoppers, etc.).

3. Streaming steam at 100 deg. C. (for the sterilisation of media).

4. Superheated steam at 115 deg. C. or 120 deg. C. (for the disinfection
of contaminated articles and the destruction of old cultivations of
bacteria).

FILTRATION.--

1. Cotton-wool filters (for the sterilisation of air and gases).

2. Porcelain filters (for the sterilisation of various liquids).

METHODS OF APPLICATION.

~Chemical Reagents~, such as belong to the class known as antiseptics (_i.
e._, substances which inhibit the growth of, but do not destroy,
bacterial life), are obviously useless. Disinfectants or germicides (_i.
e._, substances which destroy bacterial life), on the other hand, are of
value in the disinfection of morbid material, and also of various pieces
of apparatus, such as pipettes, pending their cleansing and complete
sterilisation by other processes. To this class (in order of general
utility) belong:

Lysol, 2 per cent. solution;
Perchloride of mercury, 0.1 per cent. solution;
Carbolic acid, 5 per cent. solution;
Absolute alcohol;
Ether;
Chloroform;
Camphor;
Thymol;
Toluol;
Volatile oils, such as oil of mustard, oil of garlic.

Formaldehyde is a powerful germicide, but its penetrating vapor
restricts its use. These disinfectants are but little used in the final
sterilisation of apparatus, chiefly on account of the difficulty of
effecting their complete removal, for the presence of even traces of
these chemicals is sufficient to so inhibit or alter the growth of
bacteria as to vitiate subsequent experiments conducted by the aid of
apparatus